The present invention relates to a parking-brake-operation indicator for a parking brake that performs braking operation through a cable by manually operating a brake-operation tool of a vehicle. The present invention also relates to a method of adjusting a parking brake in a vehicle having such operation indicator.
Japanese Patent Application Publication No. 60-25841 discloses that in a structure that an operating force of the parking brake is transmitted to the brake portion of the parking brake through a control cable, a signal for the braking force of the parking brake and a signal for inclination of a vehicle are compared and then a signal for driving an indicator is outputted. According to this art, it is confirmed that the parking brake is operated with the braking force corresponding to the inclination of the vehicle when the vehicle is parked on a slope.
Japanese Patent Application Publication No. 60-25841 also discloses a deformation sensor connected to a brake shoe or a brake pad for sensing deformation, a tension sensor for sensing tension of a control cable and a position sensor provided at a parking lever (or a brake-operation tool), as a braking-force sensor for sensing a braking force of the parking brake.
Japanese Utility Model Application Publication No. 61-85565 discloses that a strain gauge is attached to a piston of the brake pad that is connected to the handle of the parking brake and operable to press a brake disc, thereby sensing deformation due to the pressure of the braking pad with respect to the brake disc.
Japanese Utility Model Application Publication No. 61-85565 discloses a structure including an amplifier that outputs amplified electric voltage commensurate with a braking pressure based on resistance change of the strain gauge and a comparator that switches to ON when the outputted electric voltage becomes a reference value or less. According to this structure, an operation lamp is not turned off until locking state is fully released. Thus, the operation lamp indicates to an operator that the parking brake is fully released.
In the above parking brakes, the tension of the cable that connects the brake-operation tool to the parking brake (or the braking portion) may be adjusted in order to adjust the braking force of the parking brake or the operating force of the brake-operation tool.
However, the cable may be excessively tightened depending on the adjustment of the cable tension, which causes narrow clearances between the brake discs of the parking brake. A mechanism for adjusting the cable tension is often located at a distance from the brake discs. Thus, the cable tends to be easily excessively tightened. When the brake discs are not in contact with each other but the clearances therebetween is narrow, drag torque of the parking brake becomes large due to oil viscosity, especially in a wet type multi-disc brake.
In this regard, the braking-force sensor of Japanese Patent Application Publication No. 60-25841 and the strain gauge of Japanese Utility Model Application Publication No. 61-85565 cannot detect that the clearances between the parking discs of the parking brake are narrow.